There is a Rocky Mountain pass along Clear Creek in Colorado that is very steep, and for a long time flummoxed the railroad engineers that wanted to lead the train up to the higher altitude silver mines (Silver Plume, etc.), so the silver could come out and the necessaries come in without having to be transported on long 'mule trains'. Many times a mule or donkey (called 'burro' from the Spanish) couldn't get through the high passes during the winters, and a railroad could also take so much more weight. But Georgetown was a steep, steep problem (since locomotives can't go up as steep hills as mules, diesel trucks, and mountain goats).
So they built the railroad, got the silver out and the people in. In the late 1800s this was one of the wonders of the world and railroad tourists came here just to see the trains pass across the valley.
The rail was narrower than normal, narrow gauge (in Swedish: smalspår = small track), which is common in the mountains. It was both cheaper and better, since trains were lighter and could also turn sharper corners if they had less space between their wheels. When the railroads closed down and went bankrupt (for several reasons, more on this later), the trestle and rails rusted away and were taken down. In the 1970s some real railfans (that is their nick name) decided to build up an exact replica of the Georgetown Loop and put in the rails ago to let the trains run. They raised the money, built it, and here it is again. So you can see it, with original steam trains on it. Of course we went there on our Colorado trip for a short stop on our way into the mountains.